1. Field of the Invention
The present invention relates to an antitheft device and, more particularly, to an antitheft device for locking the steering shaft of a motor vehicle.
2. Description of the Prior Art
Antitheft devices known heretofore are operated by means of a cylinder lock and are provided with a latch which is brought into a locking position by a spring when the ignition key is extracted from the rotating cylinder portion of the lock. A rod is associated with the latch, said rod being slidingly mounted in an axial hole of a stationary cylinder portion of the lock and co-operating with a stop element axially movable with said rod during the unlocking movement of the latch and radially movable with respect to said rod at the end of the unlocking movement of the latch. The locking and unlocking mechanism comprises a first control member carried by the lock and projecting in said axial hole of the stationary cylinder and a second control member carried by said rod, the relative position of the stop element with respect to one of the two control members depends on the presence of the key in the lock. The stop element prevents the accidental movement of the latch into the locking position when the key is inserted in the rotating cylinder of the lock.
An antitheft device of the above described type is disclosed in the Italian Pat. No. 895,981 wherein the stop element consists of a movable roller loosely fitted in a window provided in the rod of the latch. The roller is retained by a leaf spring carried by the rod of the latch and is able to cooperate with a control ratchet sliding radially in a radial hole of the stationary cylinder and ending in the key slot of the rotating cylinder of the lock. The ratchet has a wedge-shaped outer end which, when the key is inserted in the key slot and the ratchet is radially moved, comes into the path of the roller carried by the rod of the latch. During the unlocking movement of the latch, the contact between the end of the ratchet and the surface of the roller causes a radial outward displacement of said roller against the action of said leaf spring, so as to enable the roller to jump onto the ratchet, said roller being then engaged between the end of the ratchet and a heel-shaped part adjacent to the window of the rod, whereby the latch is blocked in its unlocked position. The extraction of the key from the rotating cylinder of the lock causes a radial inward displacement of the ratchet and thereby a disengagement of the roller from said ratchet, so as to enable the latch to be driven into the locking position.
The above described known antitheft device comprises a large number of parts, so that the manufacture of said device is complex and expensive. Moreover, since the blocking of the latch in its unlocked position is made possible by the presence of an elastic element which is easily subject to wear, the device has a poor degree of reliability.